Implementation of octave repeat in a computor organ

ABSTRACT

In an organ or other musical instrument, octave repeat is an effect wherein tones alternately are produced at the nominal selected pitch and at an octave thereof. Herein, apparatus is disclosed for implementing octave repeat in a computor organ of the type wherein musical notes are generated by computing the amplitudes at successive sample points of a musical waveshape and converting the amplitudes to sounds as the computations are carried out in real time. Octave repeat control circuitry causes the instrument alternatively to synthesize nominal pitch and octave tones at an alternation rate established by an octave repeat clock. The amplitude envelope of each repeated tone is established by a set of attack/decay scale factors, stored in a memory and repetitively accessed by an attack/decay rate control circuit each time the octave repeat control circuitry directs pitch alternation. Note production continues during a sustain interval subsequent to instrument key release. In this sustain interval, the maximum amplitude of the repeated tones gradually is reduced by a sustain scale factor programmed by a sustain rate control circuit.

United States Patent 1191 Deutsch et al.

Oct. 7, 1975 IN A COMPUTOR ORGAN IMPLEMENTATION OF OCTAVE REPEAT Inventors: Ralph Deutsch, Sherman Oaks; Glen R. Griffith, Westminster, both of Kaisha, Hamamatsu, Japan Jan. 1 l, 1974 Appl. No.: 432,683

Nippon Gakki Seizo Kabushiki 3,809,792 /1974 Deutsch 84/124 Primary Examiner-Stephen J. Tomsky Assistant Examiner-Stanley J. Witkowski Attorney, Agent, or Firml-Ioward A. Silber [57] ABSTRACT In an organ or other musical instrument, octave repeat is an effect wherein tones alternately are produced at the nominal selected pitch and at an octave thereof. Herein, apparatus is disclosed for implementing octave repeat in a computor organ of the type wherein [52] U.S. Cl. 84/1.03; 84/1.l3; 84/l.24; musical otes are generated by computing the ampli- 34/1 26 tudes at successive sample points of a musical wave- 51 Int. Cl. GOIH 1/02; 0011! 5/00 shape and converting the amplitudes to sounds as the [58] Field of Search 84/1.01, 1.03, 1.13, 1.24, computations are carried out in real time- OCtave 34/116 DIG. 2 peat control circuitry causes the instrument alternatively to synthesize nominal pitch and octave tones at [56] Refer nces Cited an alternation rate established by an octave repeat UNITED STATES PATENTS clock. The amplitude envelope of each repeated tone 3,476,864 11/1969 Munch, Jr. et al. 84 1.03 estaihshed by a Set of F s factors 3 515 792 6/1970 Deutsch 84/1 03 stored 1n a memory and repetitively accessed by an at- 3IS49777 2/1970 Bunger": 84/1:03 tack/decay rate control circuit each time the octave 3,549,778 12/1970 Munch, Jr-

s4/L03 repeat control circuitry directs pitch alternation. Note 3,553,335 1/1971 Bunger 84/l.03 Production continues during a Sustain interval Subse- 3,610,805 /1971 Watson et a1 84/1.l3 quent to instrument key release. In this sustain inter- 0,806 10/1971 Deutsch 84/126 val, the maximum amplitude of the repeated tones 3,309,786 5/1974 gradually is reduced by a sustain scale factor pro- 3,809,788 5/1974 Deutsch 84/1.0l grammed by a Sustain rate control circuit 3,809,789 5/1974 Deutsch 84/1.0l 3,809,790 5/1974 Deutsch 84/101 23 Claims, 13 Drawing Figures 75 Mmoav EP' mm 9' W.

i 7 M "'72:; c gg' 'g'gz- 50.) D(t) Cn HRRMONIC AMPLITUDE ACCUMULATOR M Z CALI? MULTIPLIER u d 73 at) D: 7/ s1nnqR or sin ncflP MR 74 561 K56 GATE 46 69 I 56a 40 v 5g DIGITAL To a7 QUBTMN ATTACK/DELAY ANALOG A! ecnte FACTOR msmowv CONVERTER crow Mimoilv I nq'l? or nqQW l MEMORV umzmomc s T 2:5,? 27:: -57 a5 INTERVAL CLEAR RATE -w CONTROL ADDED 27 23 CONTROL 60 35 x END or sue-mm REPEAT ,'22 cm 26 ;T/= m5 kw 53L -65 571 I E CONTROL 532 55 qR q i OCTAVE I LEFI srnm' eusram i as en-r T F/;: 5m" sun-'7' REGISTER 1: 7 K be I cuocu 1 (01: Mumwuzn) 55m COUNTER 2/) 28 54 5] 32 l-a2 r C1 C1 2Q INSTRUMENT 15- D- FREQUENCY NOTE KEYBOARD 1 NUMBER (12) Gore INTERVAL 57 h SWITCHES) e LOGIC 6 MEMORY ADDER 30 CLOCK TO acmzss 24 CONTROL '75 US. Patent 0a. 7,1975 Sheet 101-5 3,910,150

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.W\ 5 8% Q UHN MUN 96 Qmmww Kama Oct. 7,1975 Sheet 2 of 5 3,910,150

US. Patent MN JONFZOU US. Patent Oct. 7,1975 Sheet4 0f5 3,910,150

US. atent Oct. 7,1975 Sheet5of5 3,910,150

IMPLEMENTATION OF OCTAVE REPEAT IN A COMPUTOR ORGAN BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to implementation of octave repeat in a computor organ.

2. Description of the Prior Art Octave Repeat" is a term used herein to designate a variety of musical effects, including hurdy-gurdy", wherein a note is repetitively. alternately sounded at the selected pitch and at the octave of that pitch. The waveform 10 of FIG. 1A illustrates a typical octave repeat sound. While the note selection key is depressed, the instrument first produces a tone at the nominal (eight-foot) pitch. This tone decreases in amplitude with a characteristic decay 10d. When the eight-foot pitch has substantially decayed to zero, a new (fourfoot) tone is generated at a pitch one octave higher. Immediately the octave tone begins to decay at a like or different decay rate. Like nominal pitch and octave tones continue to be generated alternately until the key is released.

An object of the present invention is to implement octave repeat in a computor organ. Another objective is to produce a sustained octave repeat effect wherein tone generation continues at a gradually decreasing amplitude after the note selection key is released. Such effect also is illustrated in FIG. 1A wherein the sustain envelope 1] designates the decreasing maximum amplitude of the octave repeat sound subsequent to release of the key.

During this sustain period, alternate eight-foot and four-foot tones continue to be produced. However, the maximum amplitude of successive tones gradually decreases until the tone dies out.

Other octave repeat effects are illustrated in FIGS. 2Aand 3A. As indicated by the waveshape l2, production ofthe alternate tone may begin before the previous tone has completely decayed out. In FIG. 3A, each new tone does not start abruptly at maximum amplitude. Thus the waveform 13 includes an attack portion 13a during which the amplitude rises, followed by a longer decay period 13d. The same or different attack and decay rates may characterize the alternate octave tones. Another objective of the present invention is to implement such varied octave repeat effects in an electronic musical instrument.

As used herein, the term octave repeat" also refers to effects similar to those just described, but wherein the alternately generated tones are of other than octave relationship. For example, marimba repeats involve the alternate production of the nominal pitch and a sixth thereof. A sixth is six notes up, (including the nominal pitch) in the diatonic scale. Thus e.g., the repeated sixth tones may be C and A A further object of this invention is to provide apparatus for generating such effects where the repeated tones are in other than octave relationship.

SUMMARY OF THE INVENTION In a COMPUTOR ORGAN of the type described in the inventors copending patent application Ser. No. 225,883. now US. Pat. No. 3,809,786 musical notes are produced by computing in real time the amplitudes X,,(qR) at successive sample points qR of a musical waveshape, and converting these amplitudes to notes the computations are carried out. Each sample point amplitude is computed during a regular time interval 1 according to the relationship 6",, sin (Eq. 1

where q is an integer incremented each time interval t the value n l,2,3,...W=N/2 represents the order of the Fourier component being evaluated, and C,, is a coefficient establishing the relative amplitude of the 11 component.

The period of the computed waveshape, and hence the fundamental frequency of the generated note, is established by a frequency number R selected by the instrument keyboard switches. A note at twice the frequency (i.e., an octave higher) will be generated if the value 2R is used in place of the selected value R in equation 1. Thus in accordance with the present invention, octave repeat is achieved by implementing equation 1 alternately with the selected value R to produce the nominal pitch, and with the value 2R to produce the octave tone. An octave repeat clock establishes the repetition rate at which the octave tones alternate. This rate may be selected to achieve either non-overlapping octave repeat as shown in FIG. 1A or a overlapping effect as shown in FIG. 2A.

To achieve attack and decay characteristics such as those illustrated in FIGS. 1A, 2A and 3A, the amplitude coefficients C are scaled programmatically. This may be achieved by multiplying each coefficient C,, by an attack/decay scale factor D(t) which is time dependent. Advantageously the scale factors D(t) are supplied from a memory accessed by appropriate attack- /decay rate control circuitry.

To implement sustain, generation of the alternating tones is continued after release of the note selection key. During this sustain period, the amplitude coefficients C,, further are scaled by a sustain envelope scale factor S(t). This scale factor S(t) advantageously has the value of unity while the key is depressed. During the sustain period, the value S(t) gradually decreases from unity to zero.

Thus octave repeat is implemented by generating nominal pitch tones in accordance with the relationship in alternation with generation of other tones in accordance with the relationship where and where d preferably, but not necessarily, is an integer.-If d is an integer, the alternate tone will be at some whole note interval from the nominal pitch. and the value d will specify this interval in the chromaticscale. For example, if D=l2 so that k=2, the alternate tone will be an octave l2 chromatic notes) above the nominal pitch (i.e. four-foot). For a sixth', d=9 so that k=2* =1 .68. If (1 is negative. the alternate note will be lower in frequency. Thus if d=-l 2 so that k= /2 the al' ternate notes will be one octave lower (i.e., l6-foot).

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of the invention will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the several figures.

FIG. 1A is a waveshape illustrating a typical octave repeat effect including sustain.

FIGS. 18 IE illustrate certain control signals utilized in the instrument of FIG. 4.

FIGS. 2A and 3A are waveforms respectively illustrating an overlapping octave repeat, and a variation in which each tone has a non-abrupt attack.

FIGS. 28 and 3B show control signals utilized by the system of FIG. 4 during production of the octave repeat effects illustrated in FIGS. 2A and 3A.

FIG. 4 is an electrical block diagram of a computor organ configured to produce octave repeat effects.

FIG. 5 is an electrical schematic diagram of the sustain logic used by the instrument of FIG. 4.

FIG. 6 is an electrical block diagram of circuitry employed with the computor organ of FIG. 4 to provide combined decay and sustain scale factors.

FIG. 7 is an electrical block diagram of alternative circuitry for programmatically supplying the attack- /decay and sustain scale factors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention since the scope of the invention best is defined by the appended claims.

Structural and operational characteristics attributed to forms of the invention first described also shall be attributed to forms later described, unless such characteristics obviously are inapplicable or unless specific exception is made.

Octave repeat effects such as those illustrated by FIGS. IA, 2A and 3A are produced by the computor organ of FIG. 4. For each note selectedby the keyboard switches 21, the instrument l0 alternately generates a nominal-pitch tone in accordance with equation 2 and an octave pitch tone in accordance with equation 3. The alternation rate is established by "an octave repeat rate control circuit 22. The resultant sounds are reproduced by a sound system 23.

During production of both nominaland octave-pitch tones. each waveshape sample point amplitude X,,(qR) is computed during a regular time interval 1 established by a clock 24 and a counter 25 of modulo 2W. The counter 25 provides sixteen successive subinterval timing pulses l,.,, through 1, used to govern calculation of the corresponding sixteen Fourier components employed in each waveshape amplitude computation.

4 The lsignal is delayed slightly by a delay unit 26 to provide a timing signal'on a line 27.

A set of frequency numbers R corresponding to the notes of the instrument 20 is stored in a frequency number memory 28. At the end of each computation interval 1 the selected frequency number R is supplied via a gate 29 and added to the previous contents of a note interval adder 30. Thus the contents of the adder 30, supplied via a line 31, represents the value (qR) designating the waveshape sample point currently being evaluated. Preferably the note interval adder 30 is of modulo 2W, where W is the highest order Fourier component evaluated by the system 10. Satisfactory pipe organ synthesis is achieved when'W=l6 Fourier components are evaluated by the system 10.

The value (qR) is fed to a parallel-in, parallel-out shift'register 32. During generation of the nominalpitch tone, no shift is performed by the register 32 so that the output from that register on a line 33 is the same value (qR) then present on the input line 31. As discussed in more detail below, during generation of the octave tone, the shift register 32 performs a left shift by one binary bit position. This has the effect of multiplying the value (qR) by two, so that the output on the line 33 is the value (c ZR).

The value (qR) or (4 2R) present on the line 33 is added to the contents of a harmonic interval adder 35 upon occurrence of each calculation timing pulse through 1. This is accomplished by means of a gate 36 connected in the line 33 and enabled by each of the pulses 1 through r supplied via an OR gate 37. The harmonic interval adder 35 is cleared at the end of each amplitude computation interval t," 'Thus the contents TI 11' i T W ngZR sin liqR or sin corresponding to argument (nqR) or (nqZR) received via the line 38. The sinusoid table 40 comprise a read only memory storing values of at intervals of D, where D is called the resolution constant of the memory. With this arrangement, during generation of the nominal pitch tone, the value 7T sin Till/R will be supplied on a line 41 from the sinusoid table 40 during the corresponding calculation interval r,.,,,,. For example, during the interval r the value sin ngZR will be present on the line 41 during the corresponding calculation interval I during which the 11" order Fourier component is being evaluated.

The sin value present on the line 41 is multiplied by the scaled harmonic coefficient value S(!)D(t)C,, supplied on a line 42 by a harmonic amplitude multiplier 43. The product, corresponding to the amplitude of the constituent Fourier component currently being evaluated. is supplied via a line 44 to an accumulator 45. The accumulator 45 is cleared before each computation interval, so that at the end of the interval t the contents of the accumulator 45 represents the waveshape sample point amplitude X,,(qR) for the current sample point. This amplitude is provided via a gate 46 to a digital-to-analog converter 47 which supplies to the sound system 23 a voltage corresponding to the waveshape amplitude just computed. Computation of the amplitude at the next sample point subsequently is initiated, so that the analog voltage supplied from the converter 47 comprises a musical waveshape generated in real time. Operation of the shift register 32 is controlled by the octave repeat rate control circuit 22. This circuit comprises a clock 50 which establishes the octave repeat alternation rate. The clock 50 provides a pulse on a line 51 each time that the computor organ is to switch from nominal pitch to octave generation or vice versa. Thus the pulses on the line 51 comprise the repeat" signal 52 illustrated in FIG. 1B.

The repeat signal 52 is fed to the toggle (T) input of a flip-flop 53 which controls operation of the shift register 32. When a zero output is obtained from the flip-flop 53 on a line 54, no shift is performed by the register 32. In this condition. the nominal or 8-foot pitch is generated. When the flip-flop 53 is the one state, the corresponding output on a line 55 directs the shift register 32 to perform a one-bit left shift, resulting in multiplication of the value qR by two. In this condition, the octave or 4 -foot pitch is generated. Of course, the flip-flop 53 switches state each time a pulse is received at the toggle input. Thus the system 20 will alternate between generation of the nominal pitch and octave tones each time a repeat pulse 52 oecurs on the line 5 I.

A second octave (two-foot) pitch may be obtained instead of the four-foot tone by causing the shift register 32 to perform a left shift of two bits when a signal is present on the line 55. This causes the value (qR) to be multiplied by 4 in the shift register 32. Alternatively, if a sub-octave 16-foot) tone is desired instead of the eight-foot pitch. the shift register 32 may be connected to perform a right shift of one bit position when a signal is present on the line 54. Such a right shift divides the value (qR) by two. to provide the value qR/2 on the line 33. As a result. a l6-foot tone will be produced. Other variations immediately are apparent. The operation performed by the shift register 32 alternatively could be carried out by a multiplier circuit. The circuit may be configured to multiply the value (c R) by k when a signal is received on the line 55, and to multiply the quantity R) by one when a signal is received on the line 54. The use of such multiplier is advantageous in systems wherein the alternate tones are at other than octave intervals, so that multiplication is by k=2 where d is other than 12. Such a multiplier also is useful when the amplitude computations are carried out in other than binary digital form.

Attack and decay scaling of the amplitude coefficients C is governed by an attack/decay rate control circuit 57. Each time that a repeat pulse 52 is received from the octave repeat rate control 22, the control circuit 57 initiates programmatic readout of the attack- /decay scale factors D(t) from a scale factor memory 58. As discussed below in conjunction with FIGS. 6 and 7, the control circuit 57 includes a decay rate clock 59 which cooperates with a memory access control 60 to read out scale factors from the memory 58 in a timed sequence appropriate to produce the desired attack and/or decay functions such as those illustrated in FIGS. 1A, 2A and 3A.

Sustain is initiated by appropriate sustain logic 6] each time an instrument keyboard switch 21 is released. As described below in conjunction with FIG. 5, the sustain logic 6] provides a key depressed signal 62( FIG. 1C) on a line 63 during the entire time that a keyboard switch 21 is depressed. During that period, the logic 6] controls readout of the corresponding frequency number R from the memory 28. When the keyboard switch 21 is released, the sustain logic 6] provides a start sustain signal 64 (FIG. ID) on a line 65. The logic 61 also directs continued readout of the frequency number R from the memory 28 during the entire sustain period. That readout is terminated by an end of sustain signal 66 (FIG. 1E) received by the logic 6] from a line 67.

The slope of the sustain envelope 11 (FIG. 1A), and hence the duration of the sustain period, is established by a sustain rate control circuit 68. In the embodiment of FIG. 6, the sustain rate control 68 functions to modify accessing of the attack/decay scale factor memory 58 during the sustain period. In this manner the data read from the scale factor memory 58 comprises the composite scale factor value [S(t)D(t)]. The embodiment of FIG. 6 is engaged when a switch 56 (FIG. 4) is set to the position 560.

In the alternative embodiment of FIG. 7, the sustain rate control 68 programmatically reads out appropriate sustain scale factors S(t) from a memory 69. The accessed sustain scale factor S(t) is multiplied by the attack/decay scale factor D(t) obtained from the memory 58 by a sustain scaler circuit 70. The embodiment of FIG. 7 is engaged when the switch 56 (FIG. 4) is set to the position 5617.

Thus with either embodiment (FIG. 6 or FIG. 7), the combined scale factor [S(t)D(t)] is provided on a line 71 to a harmonic coefficient scaler 72. This scaler 72 functions to multiply the coefficient C,,, received on a line 73 from a harmonic coefficient memory 74, by the combined scale factor value received from the line 71. The product [S(l)D(t)C,,] is provided on the line 42 to the harmonic amplitude multiplier 43. Readout from the harmonic coefficient memory 74 is directed by a memory access control 75 which receives the calculation timing pulses through L from the counter 25.

The harmonic coefficient memory 74 advantageously comprises a read only memory containing values C,, appropriate to produce a note of desired tonal quality.

For example, Table 1 below sets forth typical harmonic coefficient values for obtaining a diapason tone.

The amplitude computation timing interval 1, is established by the pitch or frequency f of the highest note generated by the instrument and the number N of amplitude sample points for this highest frequency note. If exactly N sample point amplitudes are computed for that note, the computational time interval t, is given by:

For example, the highest eight-foot'pitch on a standard organ keyboard is C; which has a fundamental frequency f 2.093 kHz. To accomplish accurate sampled amplitude synethesis of a note containing 16 harmonics (W=16), the waveshape should be evaluated at at least 32 sample points per cycle. Thus if the note C is evaluated at exactly N=32 sample points, the computational time interval is:

= 149 psec All of the Fourier components associated with each amplitude computation are calculated within this time interval 1,. Thus where sixteen components are individually, sequentially evaluated for each sample point, each component must be calculated in a time interval 1 given by:

14.9 #sec 16 0.93 ,usee (Eq. 6)

This establishes the rate of the clock 24.

Pleasing octave repeat effects are achieved with an octave repetition rate of between about four and eight alternations per second. Thus the preferred occurrence rate for the repeat pulses 52 (FIG. 1B) is between about four and eight pulses per second. Accordingly, the octave repeat clock 50 preferably generates pulses with a period of between A and Vs second. Obviously, this repeat period is very much greater than the waveshape sample point amplitude computation interval t In other words, the very many waveshape-sample points are computed to synthesize the musical tone during each octave repeat interval.

The sustain period preferable is between about 1 and 4 seconds. This is the time interval between occurrence of the start sustain signal 64 (FIG. 1D) and the end of sustain signal 66 (FIG. 1E).

FIG. 5 shows exemplary sustain logic 61. A flip-flop 78 is associated with each instrument keyboard switch 21. Thus if the note C is selected, the corresponding switch 21-1 is closed, providing a voltage +V,, to the set (S) input of the associated flip-flop 725-]. This causes the flip-flop 78-1 to provide a one output on a line 79-1 to the frequency number memory 28. As a result, the R number associated with theselected note C is accessed from the memory 28 and gated to the note interval adder 30 as described above. Similarly, closure of the switch 21-2 or 21-j sets the corresponding flipflop 78-2 or 78-j to the one" state. This produces a signal on the corresponding line 79-2 or 79-j and causes read out from the memory 28 of the frequency number R associated with the selected note D or C The following Table 11 lists typical values of R for the notes C through C When any keyboard switch 21 is closed, an output. is obtained from an OR gate 80 (FIG. 5') which constitutes the key depressed signal 62 (FIG. 1C) on the line 63. When that switch 21- is released, a start sustain pulse 64 (FIG. 1D) is provided on the line by an inverter 81 and a one-shot multivibrator 82 which receive the output of the OR gate 80. When the sustain period is over, the end of sustain signal 66 (FIG. IE) on the line 67 resets the selected flip-flop 78 tothe zero state. This terminates readout of the frequency number R from the memory 28 and ends production'of the corresponding note.

An octave repeat effect having the decay and sustain characteristics typified by the waveform 10 of FIG. 1A may be produced using the implementation of FIG. 6. The scale factor memory 58 stores a set of decay scale factors D(t) which establishes the shape of the decay curve 10d (FIG. 1A). Advantageously, the scale factor D(t) ranges from unity (maximum amplitude) to some minimum value, typically zero, in m steps. Thus the memory 58' contains m" values of D(t) which are accessed during consecutive equal time intervals "established by the decay rate clock 59. Table III below lists typical values of D(t) for normal and piano-like decay curves each having m=32 steps.'

Successive decay scale factors D(t) are accessed pressed. at the beginning of each octave repeat period the 1 bit is put in the first storage position 81-1 of the shift register 81. All of the other storage positions 81-2 through 81-m contain bits. The memory 58 provides to the output line 71 the scale factor value stored in the memory position corresponding to the 1 bit in the shift register 81. Thus, when the register position 81-1 contains the 1 bit, the scale factor contained in the corresponding memory storage position 58-1 is supplied to the line 71.

TABLE 111 NORMAL DECAY PIANO DECAY Point D0) D1 (Relative Decibel (Relative Decibel Amplitude) Equivalent Amplitude) Equivalent 9 0.7941 2 0.2507 -12 10 0.7076 3 0.2507 12 l I 0.7076 3 0.2234 13 12 0.6305 4 0.1990 14 13 0.5619 5 0.1774 15 14 0.4519 5 0.1774 15 15 0.5007 6 0.1581 16 16 0.4462 7 0.1408 1 7 17 0.3976 8 0.1408 17 18 0.3543 9 0.1255 18 19 0.3157 10 0.1118 19 20 0.2813 11 0.1118 19 21 0.2234 1 3 0.0997 -20 22 0.1774 1 5 0.0888 21 3 0.1581 16 0.0791 22 2-1 (1.1255 1 8 (1.0791 22 25 0.0997 20 0.0791 22 26 0.0791 22 0.0791 22 27 0.0560 25 0.0791 22 28 0.0396 28 010791 22 29 0.0223 33 (H1791 22 0.0158 36 0.0791 22 31 0.0050 46 0.0791 "22 32 0.0031 50 0.0791 22 Upon occurrence of each repeat pulse 52 (FIG. 18) on the line 51, a flip-flop 82 in the attack/decay rate control circuit 57 is set to the 1 state. This enables an AND gate 83 to supply scale factor timing pulses from the decay rate clock 59 via-a line 84 to the shift input of the shift register 81. Occurrence of each pulse on the line 84 causes the 1 bit in the register 81 to be shifted by one position. When the 1 bit is shifted to the register position 81-2, the scale factor contained in the corresponding memory storage location 58-2 will be supplied to the line 71. The next pulse from the decay rate clock 59 will cause transfer of the 1 bit to the shift register position 81-3 with concomitant output on the line 71 of the scale factor contained in the memory location 58-3.

In this manner. the consecutive decay scale factors contained in the memory 58 and typified by the values in table 111 are supplied consecutively to the harmonic coefficient sealer 72 at a rate established by the clock 59. For a set of 32 such decay scale factors, the decay clock 59 rate advantageously is between about 7.8 msec and 3.9 msec. This corresponds to the preferred octave repeat rate of about 4 to 8 alternations per second. When the last scale factor in the memory 58 has been read from the storage location 58-m. a signal is provided from the shift register 81 via a line 85 which resets the flip-flop 82 to the "0 state. This disables the AND gate 83 and terminates the supply of shift pulses to the register 81 until occurrence of the next repeat pulse on the line 51.

In the embodiment of FIG. 6, sustain scaling is accomplished by modifying the starting location from which the scale factor memory 58 is read out. The result is that upon successive occurrences of the repeat signal 52 during the sustain period, the initial amplitude of the produced note is of successively lower value, as indicated by the portion of FIG. 1A beneath the sustain envelope 11.

Such operation is implemented through the use of a second parallel load shift register 86, the parallel outputs of which are connected to the corresponding inputs of the shift register 81. When any key is depressed, the signal 62 (FIG. 1C) on the line 63 causes a 1 bit to be loaded into the first storage position 86-1 and causes 0 bits to be loaded into all other storage positions 86-2 through 86-m and 86-0 of the shift register 86. Thus each time a repeat pulse 52 occurs on the line 51 during the key depressed period, the corresponding 1 bit is loaded from the register position 86-1 into the first position 81-1 of the shift register 81. This is the initial condition described above for access of the scale factor memory 58 prior to release of the key.

When the key is released, the resultant start sustain pulse 64 (FIG. ID) on the line sets a flip-flop 88 (FIG. 6) to the 1 state. This enables an AND gate 89 to provide timing pulses from a sustain rate clock 90 via a line 91 to the shift input of the shift register 86. Each such pulse causes the single 1 bit in the register 86 to be shifted one position. The pulse rate from the clock 90 is selected so that the 1 bit in the register 86 will be shifted from the first register position 86-1 to the last register position 86-0 in a period of between about 1 second and about 4 seconds. This corresponds to the preferred duration of sustain. In the illustrative system wherein m=32, the sustain rate clock 90 advantageously provides timing pulses with a separation of between about 31 msec and msec, corresponding to the sustain rate of between 1 and 4 seconds.

During the sustain period, occurrence of the repeat" pulse 62 causes the single 1 bit to be loaded into the shift register 81 at a position corresponding to the current location of the 1 bit in the sustain shift register 86. Thus the initial decay scale factor accessed from the memory 58 will be less than the maximum value. For example, the 1 bit initially may be loaded into the shift register position 81-3 so that consecutive readout of the memory 51 will start from the location 58-3. The resultant decay curve 10d under the sustain envelope 11 (FIG. 1A) is established by the scale factors accessed from memory location 58-3 through 58-m. Successive repeated sounds will have gradually decreasing amplitude maxima as readout of the memory 58 begins from storage location closer to the last location 58-m.

When the single 1 bit in the shift register 86 finally reaches the end position 86-0, an end of sustain signal is produced on the line 67. This signal resets the flip-flop 88 to disable the AND gate 89, terminating the sustain.

In the alternative embodiment of FIG. 7, the attack- /decay scale factor memory 58a is accessed by a parallel load shift register 6011 similar to the register 81 of FIG. 6. Occurrence of the repeat pulse 52 always loads the single 1 bit into the first position 60-1 of the shift register 60a. Thus, during both the key depressed and sustain periods, accessing of the scale factor memory 58a begins from the first storage location 93-1.

The decay rate clock 59 the flip-flop 82 and the AND gate 83 function in the same manner as the like numbered but unprimed components of FIG. 6 to provide pulses on the line 84 to the shift input of the register 60a; Each such pulse advances the single I bit by one position in the shift register 60a, thereby causing concomitant readout onto a line 94 of the scale factor in the corresponding storage location of the memory 580. The first group of storage locations 93-1 through 93-6 may contain scale factors of gradually increasing value. Utilization of these scale factors produces a nonabrupt attack such as that illustrated by the curve 13:! in FIG. 3A. Gradually decreasing decay scale factors advantageously are contained in the storage locations 93-41 through 93- of the memory 58a. Thus consecutive accessing of the memory 580 will result in an octave repeat sound characterized by the waveshape 13 of FIG. 3A.

In the embodiment of FIG. 7, sustain scaling is implemented using a separate sustain scale factor memory 69 accessed by a parallel load shift register 95 similar in operation to the shift register 60a. The key depressed signal on the line 63 causes a single I bit to be loaded into the first position 95-1 of the register 95. Advantageously the corresponding first storage location 69-1 of the memory 69 contains a scale factor of value 1.000. With this arrangement, while the key is depressed, the unity scale factor will be provided via a line 96 to the sustain scaler 70. Thus prior to the start of sustain, the attack/decay scale factors D(t) obtained via the line 94 will be provided unchanged in value to the harmonic coefficient scaler 72.

The sustain rate clock 90, the flip-flop 88 and the AND gate 89' operate like the correspondingly numbered but unprimed components of FIG. 6 to provide sustain rate timing pulses on a line 91 to the shift input of the register 95. Each such pulse causes the single 1 bitin the register 95 to be shifted one position. This causes the sustain scale factor stored in the corresponding location of the memory 69 to be read out via the line 96 to the sustain scaler 70. When the 1 bit is finally shifted to the last register position 95-0, an end of sustain signal is produced on the line 67 and the flip-flop 88 is reset to complete the sustain.

The sustain scaler 70 multiplies the attack/decay scale factor D(t) by the sustain scale factor (1) and provides the product [S(z)D(r)] via the line 71 to the harmonic coefficient scaler 72. The produced notes exhibit a gradually decreasing maximum amplitude having a sustain envelope established by the scale factor values stored in the memory 69.

The sustain scaler 70 may be implemented using a conventional integrated circuit device such as the Signetics type 8243 scaler. Alternatively, the scaler 70 may comprise a multiplier implemented using Signetics type 8202 buffer registers and type 8260 arithmetic elements, as shown in the application sheet, page 28 of Signetics catalog entitled Digital 8000 Series TTL/MSI, copyright 1971. The scale factor memories 58, '58, 58a and 69 each may be implemented using a conventional diode array memory. Alternatively, each may comprise an integrated circuit read only memory such as the Signetics type 8223. The shift registers 60a, 81., 86 and 95 each may comprise a commercially available integrated circuit, parallel in, parallel out shift register such as the Texas Instrument Co. (TI) type 7495. The same Tl type 7495 device may be used as the shift register 32 (FIG. 4).

The harmonic coefficient scaler 72 and the harmonic amplitude multiplier 43 each may be implemented in the same way as the' sustain scaler 70. The frequency number memory 28 and the harmonic coefficient memory 74 eacy may comprise a Signeticstype 8223 integrated circuit read only memory. This device includes memory addressing circuitry that can be used as the memory access control 75. The sinusoid table 40 and associated memory address decoder 39 likewise may be implemented using an integrated circuit read only memory like the Signetics type 8223 or the Texas Instrument Co. type TMS 4400, programmed to store sin values. A useful integrated circuit having prestored sinusoid table and addressing circuitry also is available from the Texas Instrument Co. asa type TMS 4405 device.

The note interval adder 30, the harmonic interval adder 35 and the accumulator 45 each may be implemented using commercially available full adders such as the Signetics type 8268 or the Texas Instrument Co. types SN 5483 or SN 7483. These may be connected as shown in the section entitled Accumulators of the textbook by Ivan Flores entitled Computer Logic, Prentice-Hall, 1960.

The particular attack, decay and sustain scale factors are a design choice, and those listed in Table III are illustrative only. The octave repeat clock 50, the decay rate clock 59, the sustain rate clock '90 and the calculation interval clock 24 are shown herein as independent devices. These clocks all may operate asynchronously. Alternatively, some or all of the clocks may operate synchronously. The overlapping effect illustrated in FIG. 2A may be obtained by making the repeat clock 50 period less than the time required to access all of the decay scale factorsfrom the memory 58 (FIG. 6). Alternatively, the minimum decay scale factor value stored in the memory 58' may be greater than zero, so that the decay curve 1017 does not decrease to zero even though all of the scale factors D(z) are accessed from the memory 58' prior tooccurrence of the next repeat pulse52.

In an alternative embodiment, the shift register 32 (FIG. 4) may be eliminated, the line 31 connected directly to the line 33, and the octave'repeat rate control 22 used to modify readout of the frequency number memory 28. With such arrangement, when the flip-flop 53 is in the 0 state, the R-number associated with the' selected note is accessed from, the memory 28. Accordingly, the value-(qR) will be supplied via thelines 31, 33 to the gate 36 and the nominal pitch tone will be produced. When the flip-flop 53 is in the} state, the frequency number (2R) associated with the octave of the selected note is accessed .from the memory 28. As

a result the contentsof the note interval adder 30.will represent the value (112R). This value will be supplied via the lines 31, 33 to the gate 36 and the octave tone will be produced. This arrangement may be implemented by storing the R numbers consecutively in groups of 12 note-related storage locations in the memory 28. When the flip-flop 53 is in the 1 state, the value 12 is added to the memory access address associated with the selected key so that the octave frequency number is accessed.

For a marimba implementation, the shift register 32 (FIG. 4) advantageously is replaced by a multiplier which multiplies the value qR by k=2"" 1.68 when a signal is present on the line 55. This results in production of a sixth tone. When a signal is present on the line 54, the value (qR) is passed unchanged from the line 31 to the line 33, so that the nominal tone is produced. For example, if the nominal tone is C,; the value R 0.5000 (see Table II). When (z R) is multiplied by 1.68,

.the product is c 1.68)R q( 1.68) (0.5000) q 0.84

which corresponds to the R number given in Table II for the sixth note A,,.

intending to claim all novel, useful and unobvious features shown or described, the applicant:

We claim:

1. An electronic musical instrument comprising: tone generation means for computing in real time the amplitudes at successive sample points of a musical waveshape, said means including first circuitry for separately evaluating the constituent Fourier component,

an accumulator for summing these components to obtain each sample point amplitude, and a converter for converting the obtained amplitudes to musical tones, the fundamental frequency of the generated tone being established by a frequency number utilized by said first circuitry in each Fourier component evaluation,

note selection switches,

a frequency number memory containing frequency number values associated with selectable notes, and

octave repeat control means, operatively connected to said frequency number memory, for alternately providing to said first circuitry a first frequency number associated with a note selected by said switches and a second frequency number associated with a different note, said tone generation means correspondingly, alternately generating tones at the nominal pitch of said selected note and at the pitch of said different note.

2. An electronic musical instrument according to claim 1, said instrument further comprising:

a harmonic coefficient memory storing a set of harmonic coefficients which establish the relative amplitudes of the individual constituent Fourier components evaluated to obtain each sample point amplitude, said harmonic coefficients thereby establishing the timbre of the generated tones,

attack/decay control means, cooperating with said octave repeat control means, for providing during each repetitive tone generation interval successive scale factors which establish the amplitude envelope of the tone generated during that interval, and

harmonic coefficient scaler means for accessing from said harmonic coefficient memory the harmonic coefficient associated with the individual constituent Fourier component currently being evaluated and for multiplying said accessed harmonic coefficient by the scale factor currently being provided by said attack/decay control means, the resultant product being a scaled harmonic coefficient that is provided to said first circuitry for utilization thereby to establish both the relative amplitudes of the evaluated Fourier components and the amplitude envelope of the generated musical waveshape. 3. An electronic musical instrument according to claim 2 wherein said attack/decay control means comprises:

a memory storing a set of attack/decay scale factors that define the amplitude envelope of the generated tone,

an attack/decay rate clock, and

memory access control circuitry for successively accessing said stored attack/decay scale factors from said memory at a rate established by said clock, said accessed scale factors being provided to said harmonic coefficient scaler means.

4. An electronic musical instrument according to claim 2 wherein said octave repeat control means comprises;

an octave repeat clock which establishes the alternation rate of the repetitive tone generation intervals, said clock providing a repeat signal at the beginning of each such interval, alternate provision of said first and second frequency numbers being controlled by said repeat signal, and wherein said attack/decay control means repetitively provides said successive scale factors beginning upon occurrence of each repeat signal.

5. An electronic musical instrument according to claim 2 further comprising:

sustain logic, operatively connected to said note selection switches and said octave repeat control means, for continuing to provide said first and second frequency numbers alternately to said tone generator means for a sustain period following release of the selected note switch so that said alternate tones continue to be generated during said sustain period, and

sustain control means, operative during said sustain period, for progressively decreasingly Scaling the attack/decay scale factors provided by said attack- /decay control means prior to utilization of said attack/decay scale factors by said harmonic coefficient sealer means.

6. An electronic musical instrument according to claim 1 further comprising:

sustain logic, operatively connected to said note selection switches and said octave repeat control means, for continuing to provide said first and second frequency numbers alternately to said tone generation means for a sustain period following release of the selected note switch so that said alternate tones continue to be generated during said sustain period, and

sustain scaler means for progressively decreasing the amplitude of the constituent Fourier components evaluated during said sustain period so that the maximum amplitude of each repeated alternately generated tone is less than that of the proceeding tone.

7. In an electronic musical instrument of the type wherein a musical waveshape is synthesized by computing in real time the amplitudes at successive sample points of that waveshape, said waveshape amplitudes being converted to musical signals as the computations are carried out, said instrument including generation means having first circuitry for individually calculating the constituent Fourier components of that musical waveshape and an accumulator for summing these Fourier components to obtain each waveshape amplitude, the relative amplitudes of said Fourier components being established by scaled amplitude coefficients derived from a set of unscaled hannonic coefficients stored in a first memory, the improvement comprising:

octave repeat control means for causing said genera- 'tion means alternately to synthesize said musical signals at a selected pitch and at an interval of said selected pitch, Y

a scale factor memory storing a set of scale factors for establishing the attack/decay characteristics of the alternately synthesized selected pitch and interval musical signals, and

a harmonic coeffieient sealer, connected to said first memory, to said scale factor memory, and to said first circuitry, for multiplying the harmonic coefficients obtained from said first memory by a scale factor obtained from said scale factor memory, the products of said multiplication being scaled amplitude coefficients that are supplied to said first circuitry for utilization thereby.

8. An electronic musical instrument according to claim 7 further comprising:

an attack/decay rate control clock, and

memory access circuitry for accessing from said scale factor memory successive ones of said set of scale factors at a rate established by said attack/decay rate control clock, said accessed scale factors being provided to said harmonic coefficient sealer, and

attack/decay control circuitry for directing said memory access circuitry to repeat said accessing of successive scale factors each time said octave repeat control means causes alternation of the synthesized pitch.

9. An electronic musical instrument according to claim 8 wherein said memory access circuitry comprises;

a first shift register containing a single 1 bit, the register positions of said first shift register havinga oneto-one correspondence with storage locations in said scale factor memory, the scale factor in the storage location corresponding to the register position of said single 1 bit being provided to said harmonic coeffieient scaler, the position of said single bitbeing incremented by timing pulses from said attack/decay ratecontrol clock.

10. An electronic musical instrument according to claim 9 further comprising:

a circuitfor progressively decreasing the maximum 7 amplitude of the selected pitch and octave musical signals during a sustain interval, comprising;

a sustain rate clock,

a second shift register storing a single 1 bit and having a one-to-one correspondence with storage loca tions in said first shift register, said single 1 bit .being in the first position of said register at the beginning of said sustain interval and being incremented in position byoutput pulses from said sustain rate clock, and

load means, operative each time said generation means is caused to synthesize an alternate pitch, for resetting the single 1 bit in said first shift register to the position corresponding to the position of the single 1 bit in the second shift register at the time of said resetting, so that successive accessing of scale factors from saidscale factor memory begins with decreasing maximum values during succeeding generated note repetitions during said sustain interval.

11. An electronic musical instrument according to claim 8 further comprising: i

note selection switches connected to said generation means for selection of thensynthesized pitch, sustain logic operatively connected to said note selection switchesand said generation-means to continue alternating synthesis of said selected pitch and interval musical'signals during a sustain interval following the release of a note selection switch,

and a a circuit for progressively decreasing the maximum amplitude of the alternately produced selected pitch and interval musical signals during said sustain interval. 12. An electronic musical instrument according to claim 11 wherein said circuit comprises; 7

another memory storing a set of sustain scale factors defining a waveshape amplitude envelope,

a sustain memory access'controller operatively connected to said other memory and to said sustain logic, for accessing successive sustain scale factors from said other memory during said sustain interval,and-

a sustain scaler for multiplying each attack/decay scale factor by said accessed sustain scale factor before said attack/decay scale factor is provided to said harmonic coeffieient scaler for utilization thereby.

13. An electronic musical instrument according to claim 12 wherein said sustain logic provides a start sustain signal when said note selection switch is released, and wherein said sustain memory access controller includes a sustain rate clock, said controller causing access of said sustain scale factors beginning upon occurrence of said startsustain" signal and continuing at a'rate established by said sustain rate clock, said controller providing an end of sustain signal at the end of said sustain interval, said sustain logic'terminating generation-of said musical signals in response to occurrence of said end of sustain signal.

14. An electronic musical instrument according to claim 7 wherein said scale factor memory contains a first subset of scale factors of progressively increasing value and a second set of scale factors of progressively decreasing value, successive accessing and utilization of said first and second subsets resulting in repeated selected pitch and octave musical sounds each having a non-abrupt attack followed by a non-abrupt decay amplitude envelope.

15. An electronic musical instrument accordingto claim 7 wherein said attack/decay scale factors are accessed from said scale factor memory successively beginning from a selected-starting location in said memory, together with means for controlling said selected starting location as a function of time.

16. An electronic musical instrument comprising:

note selection switches,

a tone generator which produces a tone at a pitch established by a signal provided thereto, the amplitude envelope of said produced tone being established by scale'factors provided thereto, said scale factors having values which change intime so as to define a predetermined amplitude envelope for the generated tone,

octave repeat control means, operatively connected to said note selection switches, for alternately providing to said'tone generator a first pitch establishing signal associated with a note selected by said switches and a second pitch establishing signal associated with an interval of said selected note, said tone generator correspondingly, alternately generating tones at the nominal pitch of said selected note and at the pitch of said interval, and

attack/decay control means, operatively connected to said octave repeat control means, for providing to said tone generator during each repetitive tone generation period successive ones of said scale factors to establish the amplitude envelope of the tone generated during the period.

17. An electronic musical instrument wherein tones at the nominal pitch of a selected note and at an interval thereof alternately are produced. comprising:

first means for computing at regular time intervals I,

the amplitudes X,,(qR) of a waveshape, where q is an integer incremented each time interval t,, in accordance with the relationship wherein n=l,2,3, W designates the order of the Fourier components included in each waveshape amplitude computation, where C is a coefficient establishing the relative amplitude of the corresponding n component, wherein R is a number specifying the period of the selected nominal pitch tone, where and z! is a constant specifying the interval between said nominal pitch and interval tones, d having the value during production of the nominal pitch tone and having a value other than zero during production of the inter: val tone, wherein DH) is a scale factor, the value of which varies in time, that establishes the attack/decay characteristics of each repeated tone and wherein S(t) is a scale factor which is unity except during a sustain period, said first means comprising;

octave repeat rate control circuitry alternately providing first and second signals indicating respectively that the nominal pitch or the interval tone is to be produced, first circuitry operative during occurrence of said nominal pitch indicating first signal for providing the values 11 sin TIM/R for each order 11 during subintervals of each computation interval 1, for the value R associated with the selected note, I

second circuitry operative during occurrence of said interval tone indicating second signal for providing the values I 71' sin TIMI/(R.

with d having said other value, for each order n during subintervals of each computation interval 1 for the value R associated with the selected note.

attack/decay scale factor circuity providing a signal indicative of the product {S(t)D(t)C,,}during production of each tone, the coefficientC beign supplied in correspondence with theorder n of the sin 5 values provided by said first and second circuitry, the scale factor D(t) being scaled repetitively on each occurrence of said alternately provided first and second signals from said octave repeat rate control circuitry. harmonic amplitude multiplier which multiplies each sin value provided by said first and second circuitry by the corresponding product {S(t)D(t)C,,} from said attack/decay scale factor circuitry, and

an accumulator for summing during each computationinterval t, the products from said harmonic amplitude multiplier to obtain each waveshape amplitude X,, (qR), and

second means responsive to said first means for providing musical tones from said obtained amplitudes, said musical tones exhibiting an octave repeat effect.

18. An electronic musical instrument according to claim 17 wherein said first means further comprises;

a frequency number memory storing a set of values R for selectable notes,

note selection switch circuitry for accessing from said frequency number memory a value R associated with a selected switch,

a note interval adder incremented by the accessed value R at each time interval t, to obtain the value qR, and

multiplier circuitry operatively connected to said octave repeat rate control circuitry for multiplying said obtained value qR by K=d/l2 where d has said other value only during occurrence of said interval tone indicating signal.

19. An electronic musical instrument according to claim 17 wherein said first means further comprises:

a frequency number memory storing values of R for selectable notes, said values being stored in octaverelated subsets of twevle,

note selection switches, and

access circuitry operatively connected to said octave repeat rate control circuitry, for accessing from said frequency number memory the value of R associated with the note selected by said switches during occurrence of said nominal pitch indicating signal, and for accessing the value (kR) associated with said interval of said note selected by said switches during occurrence of said interval tone indicating signal.

20. An electronic musical instrument according to claim 17 wherein said attack/decay scale factor circuitry comprises;

an attack/decay scale factor memory storing a set of scale factor values O(t) an attack/decay rate control, incuding a rate control clock, forjsuccessively accessing said scale factors from the attack/decary scale factor memory at a rate established by said rate control clock, said successive accessing beginning repetitively in response to each occurrence of said alternating signals from said octave repeat rate control circuitry.

21. An electronic musical instrument according to claim 20 wherein the entire set of stored scale factor values D(t) is accessed from said attack/decay scale sustain logic, operatively connected to said first means, for continuing tone production during a sustain period beginning upon release of a note selection key,

said sustain scaler including a sustain rate clock and being operative, during said sustain period, to direct access of gradually decreasing subsets of said stored scale factors from said attack/decay scale factor'memory, thereby progressively decreasing the maximum amplitude of the repeated nominal pitch and interval tones in response to successive timing signals from said sustain rate clock.

23. An electronic musical instrument according to claim 20 and further comprising;

a sustain scale factor memory storing a set of sacle factors S(t), i

a sustain rate control, including sustain rate control clock, for successively accessing said scale factors S(t) from said sustain scale factor memory, at a rate established by said slustain rate control clock, during said sustain period, and

a sustain scaler for multiplying the attack/decay scale factor D(tl) accessed from said attach/ decay scale factor memory by the sustain scale factor S(t) concurrently accessed from said sustain scale factor memory, and for providing the product S(t)D(t) to said attack/decay scale factor 

1. An electronic musical instrument comprising: tone generation means for computing in real time the amplitudes at successive sample points of a musical waveshape, said means including first circuitry for separately evaluating the constituent Fourier component, an accumulator for summing these components to obtain each sample point amplitude, and a converter for converting the obtained amplitudes to musical tones, the fundamental frequency of the generated tone being established by a frequency number utilized by said first circuitry in each Fourier component evaluation, note selection switches, a frequency number memory containing frequency number values associated with selectable notes, and octave repeat control means, operatively connected to said frequency number memory, for alternately providing to said first circuitry a first frequency number associated with a note selected by said switches and a second frequency number associated with a different note, said tone generation means correspondingly, alternately generating tones at the nominal pitch of said selected note and at the pitch of said different note.
 2. An electronic musical instrument according to claim 1, said instrument further comprising: a harmonic coefficient memory storing a set of harmonic coefficients which establish the relative amplitudes of the individual constituent Fourier components evaluated to obtain each sample point amplitude, said harmonic coefficients thereby establishing the timbre of the generated tones, attack/decay control means, cooperating with said octave repeat control means, for providing during each repetitive tone generation interval successive scale factors which establish the amplitude envelope of the tone generated during that interval, and harmonic coefficient scaler means for accessing from said harmonic coefficient memory the harmonic coefficient associated with the individual constituent Fourier component currently being evaluated and for multiplying said accessed harmonic coefficient by the scale factor currently being provided by said attack/decay control means, the resultant product being a scaled harmonic coefficient that is provided to said first circuitry for utilization thereby to establish both the relative amplitudes of the evaluated Fourier components and the amplitude envelope of the generated musical waveshape.
 3. An electronic musical instrument according to claim 2 wherein said attack/decay control means comprises; a memory storing a set of attack/decay scale factors that define the amplitude envelope of the generated tone, an attack/decay rate clock, and memory access control circuitry for successively accessing said stored attack/decay scale factors from said memory at a rate established by said clock, said accessed scale factors being provided to said harmonic coefficient scaler means.
 4. An electronic musical instrument according to claim 2 wherein said octave repeat control means comprises; an octave repeat clock which establishes the alternation rate of the repetitive tone generation intervals, said clock providing a ''''repeat'''' signal at the beginning of each such interval, alternate provision of said first and second frequency numbers being controlled by said ''''repeat'''' signal, and wherein said attack/decay control means repetitively provides said successive scale factors beginning upon occurrence of each ''''repeat'''' signal.
 5. An electronic musical instrument according to claim 2 further comprising: sustain logic, operatively connected to said note selection switches and said octave repeat control means, for continuing to provide said first and second frequency numbers alternately to said tone generator means for a sustain period following release of the selected note switch so that said alternate tones continue to be generated during said sustain period, and sustain control means, operative during said sustain period, for progressively decreasingly scaling the attack/decay scale factors provided by said attack/decay control means prior to utilization of said attack/decay scale factors by said harmonic coefficient sealer means.
 6. An electronic musical instrument according to claim 1 further comprising: sustain logic, operatively connected to said note selection switches and said octave repeat control means, for continuing to provide said first and second frequency numbers alternately to said tone generation means for a sustain period following release of the selected note switch so that said alternate tones continue to be generated during said sustain period, and sustain scaler means for progressively decreasing the amplitude of the constituent Fourier components evaluated during said sustain period so that the maximum amplitude of each repeated alternately generated tone is less than that of the proceeding tone.
 7. In an electronic musical instrument of the type wherein a musical waveshape is synthesized by computing in real time the amplitudes at successive sample points of that waveshape, said waveshape amplitudes being converted to musical signals as the computations are carried out, said instrument including generation means having first circuitry for individually calculating the constituent Fourier components of that musical waveshape and an accumulator for summing these Fourier components to obtain each waveshape amplitude, the relative amplitudes of said Fourier components being established by scaled amplitude coefficients derived from a set of unscaled harmonic coefficients stored in a first memory, the improvement comprising: octave repeat control means for causing said generation means alternately to synthesize said musical signals at a selected pitch and at an interval of said selected pitch, a scale factor memory storing a set of scale factors for establishing the attack/decay characteristics of the alternately synthesized selected pitch and interval musical signals, and a harmonic coefficient scaler, connected to said first memory, to said scale factor memory, and to said first circuitry, for multiplying the harmonic coefficients obtained from said first memory by a scale factor obtained from said scale factor memory, the products of said multiplication being scaled amplitude coefficients that are supplied to said first circuitry for utilization thereby.
 8. An electronic musical instrument according to claim 7 further comprising: an attack/decay rate control clock, and memory access circuitry for accessing from said scale factor memory successive ones of said set of scale factors at a rate established by said attack/decay rate control clock, said accessed scale factors being provided to said harmonic coefficient scaler, and attack/decay control circuitry for directing said memory access circuitry to repeat said accessing of successive scale factors each time said octave repeat control means causes alternation of the synthesized pitch.
 9. An electronic musical instrument according to claim 8 wherein said memory access circuitry comprises; a first shift register containing a single 1 bit, the register positions of said first shift register having a one-to-one correspondence with storage locations in said scale factor memory, the scale factor in the storage location corresponding to the register position of said single 1 bit being provided to said harmonic coefficient scaler, the position of said single 1 bit being incremented by timing pulses from said attack/decay rate control clock.
 10. An electronic musical instrument according to claim 9 further comprising: a circuit for progressively decreasing the maximum amplitude of the selected pitch and octave musical signals during a sustain interval, comprising; a sustain rate clock, a second shift register storing a single 1 bit and having a one-to-one correspondence with storage locations in said first shift register, said single 1 bit being in the first position of said register at the beginning of said sustain interval and being incremented in position by output pulses from said sustain rate clock, and load means, operative each time said generation means is caused to synthesize an alternate pitch, for resetting the single 1 bit in said first shift register to the position corresponding to the position of the single 1 bit in the second shift register at the time of said resetting, so that successive accessing of scale factors from said scale factor memory begins with decreasing maximum values during succeeding generated note repetitions during said sustain interval.
 11. An electronic musical instrument according to claim 8 further comprising: note selection switches connected to said generation means for selection of the synthesized pitch, sustain logic operatively connected to said note selection switches and said generation means to continue alternating synthesis of said selected pitch and interval musical signals during a sustain interval following the release of a note selection switch, and a circuit for progressively decreasing the maximum amplitude of the alternately produced selected pitch and interval musical signals during said sustain interval.
 12. An electronic musical instrument according to claim 11 wherein said circuit comprises; another memory storing a set of sustain scale factors defining a waveshape amplitude envelope, a sustain memory access controller operatively connected to said other memory and to said sustain logic, for accessing successive sustain scale factors from said other memory during said sustain interval, and a sustain scaler for multiplying each attack/decay scale factor by said accessed sustain scale factor before said attack/decay scale factor is provided to said harmonic coefficient scaler for utilization thereby.
 13. An electronic musical instrument according to claim 12 wherein said sustain logic provides a ''''start sustain'''' signal when said note selection switch is released, and wherein said sustain memory access controller includes a sustain rate clock, said controller causing access of said sustain scale factors beginning upon occurrence of said ''''start sustain'''' signal and continuing at a rate established by said sustain rate clock, said controller providing an ''''end of sustain'''' signal at the end of said sustain interval, said sustain logic terminating generation of said musical signals in response to occurrence of said ''''end of sustain'''' signal.
 14. An electronic musical instrument according to claim 7 wherein said scale factor memory contains a first subset of scale factors of progressively increasing value and a second set of scale factors of progressively decreasing value, successive accessing and utilization of said first and second subsets resulting in repeated selected pitch and octave musical sounds each having a non-abrupt attack followed by a non-abrupt decay amplitude envelope.
 15. An electronic musical instrument according to claim 7 wherein said attack/decay scale factors are accessed from said scale factor memory successively beginning from a selected starting location in said memory, together with means for controlling said selected starting location as a function of time.
 16. An electronic musical instrument comprising: note selection switches, a tone generator which produces a tone at a pitch established by a signal provided thereto, the amplitude envelope of said produced tone being established by scale factors provided thereto, said sCale factors having values which change in time so as to define a predetermined amplitude envelope for the generated tone, octave repeat control means, operatively connected to said note selection switches, for alternately providing to said tone generator a first pitch establishing signal associated with a note selected by said switches and a second pitch establishing signal associated with an interval of said selected note, said tone generator correspondingly, alternately generating tones at the nominal pitch of said selected note and at the pitch of said interval, and attack/decay control means, operatively connected to said octave repeat control means, for providing to said tone generator during each repetitive tone generation period successive ones of said scale factors to establish the amplitude envelope of the tone generated during the period.
 17. An electronic musical instrument wherein tones at the nominal pitch of a selected note and at an interval thereof alternately are produced, comprising: first means for computing at regular time intervals tx the amplitudes Xo(qR) of a waveshape, where q is an integer incremented each time interval tx, in accordance with the relationship
 18. An electronic musical instrument according to claim 17 wherein said first means further comprises; a frequency number memory storing a set of values R for selectable notes, note selection switch circuitry for accessing from said frequency number memory a value R associated with a selected switch, a note interval adder incremented by the accessed value R at each time interval tx to obtain the value qR, and multiplier circuitry operatively connected to said octave repeat rate control circuitry for multiplying said obtained value qR by K d/12 where d has said other value only during occurrence of said interval tone indicating signal.
 19. An electronic musical instrument according to claim 17 wherein said first means further comprises: a frequency number memory storing values of R for selectable notes, said values being stored in octave-related subsets of twevle, note selection switches, and access circuitry operatively connected to said octave repeat rate control circuitry, for accessing from said frequency number memory the value of R associated with the note selected by said switches during occurrence of said nominal pitch indicating signal, and for accessing the value (kR) associated with said interval of said note selected by said switches during occurrence of said interval tone indicating signal.
 20. An electronic musical instrument according to claim 17 wherein said attack/decay scale factor circuitry comprises; an attack/decay scale factor memory storing a set of scale factor values O(t) an attack/decay rate control, incuding a rate control clock, for successively accessing said scale factors from the attack/decary scale factor memory at a rate established by said rate control clock, said successive accessing beginning repetitively in response to each occurrence of said alternating signals from said octave repeat rate control circuitry.
 21. An electronic musical instrument according to claim 20 wherein the entire set of stored scale factor values D(t) is accessed from said attack/decay scale factor memory between successive occurrences of said alternating signals except during said sustain period, and further comprising; third circuitry, operative during said sustain period and connected to said attack/decay rate control, for causing less than said entire set of stored scale factor values D(t) to be accessed from said attack/decay scale factor memory between successive occurrences of said alternating signals during said sustain period.
 22. An electronic musical instrument according to claim 21 and having note selection keys, further comprising; sustain logic, operatively connected to said first means, for continuing tone production during a sustain period beginning upon release of a note selection key, said sustain scaler including a sustain rate clock and being operative, during said sustain period, to direct access of gradually decreasing subsets of said stored scale factors from said attack/decay scale factor memory, thereby progressively decreasing the maximum amplitude of the repeated nominal pitch and interval tones in response to successive timing signals from said sustain rate clock.
 23. An electronic musical instrument according to claim 20 and further comprising; a sustain scale factor memory storing a set of sacle factors S(t), a sustain rate control, including a sustain rate control clock, for successively accessing said scale factors S(t) from said sustain scale factor memory, at a rate established by said sustain rate contrOl clock, during said sustain period, and a sustain scaler for multiplying the attack/decay scale factor D(tl ) accessed from said attach/decay scale factor memory by the sustain scale factor S(t) concurrently accessed from said sustain scale factor memory, and for providing the product S(t)D(t) to said attack/decay scale factor circuitry. 